The invention concerns an adhesive application station for binding stacked printed products by means of a liquid or liquefiable adhesive, where the application station comprises an application head for the adhesive with a slip surface for the printed products, and on both sides of this slip surface a stop for these printed products and a slot nozzle extending over the entire width of the slip surface for the adhesive, an adhesive reservoir formed as a pressure chamber and means for generating a pressure in the adhesive reservoir.
For production of books, magazines, brochures etc. printed products of all types are first stacked and fixed in a holder. Then the so-called spine is milled flat and simultaneously roughened. In this way the subsequently applied adhesive can adhere better. Insufficient adhesion of the adhesive leads to poor binding quality, the bound printed products fall apart in use or individual leaves become detached. The applied adhesive layer must, however, not only firmly bind each individual page but also be sufficiently resilient to allow easy leaving through the bound printed products.
The application of adhesive with a brush or equivalent means as practised originally was simplified as developments advanced so that the prepared spine of a stack could be drawn over at least one roller immersed in an adhesive bath. However, this open system still has the disadvantage that, for example in the case of a moisture-reactive polyurethane adhesive, the physical and chemical properties could change under the effects of air and heat. The same or similar problems can occur in all known adhesives which are used as cold adhesives, hot adhesives or hot melts (thermoplastic adhesives). Advantageously, economical and ecological considerations have led for example to watery polyurethane dispersions, known in brief as PU dispersions. The term PU indicates a group of high molecular materials which are produced by poly-addition of di-isocyanates and bi- or multi-functional hydroxyl compounds. In their molecules the basic modules are linked by the urethane group (xe2x80x94NHxe2x80x94COOxe2x80x94). Depending on the chemical nature of the original compounds used, polyurethanes are obtained with linear, branched or cross-linked macro-molecules. Linear polyurethanes are thermoplastic substances which have multiple applications. Here we are interested only in cross-linked elastomer polyurethanes which are suitable as resilient, water- and heat-resistant adhesives.
Adhesive application stations are known which work with slot nozzles. The prepared spine of a stack of printed products is drawn between two stops over a slip surface with an outlet slot for the adhesive. The slot nozzle discharges adhesive during this short period. Although stacks with the same number of printed products are drawn through in succession, these stacks do not have precisely the same width. In special cases the different stack widths can deviate by up to xc2x11 mm. Even within one and the same stack, width differences of the order of a few tenths of millimeters can occur. In practice the result is recurrent problems, for example with adhesive strings on the bound printed product.
EP 0 550 913 A1 describes an adhesive application station with two jaws manually adaptable to various stack heights and forming the side guide jaws. For slightly different stack heights at least one screw must be adjusted or the play between the jaw and the stack taken into account. This leads to greater cost or the formation of unattractive adhesive strings. To eliminate this disadvantage a sealing block is inserted in each jaw.
The invention is therefore based on the task of creating an adhesive application station for binding stacked printed products of the type described initially which eliminates the problems with different stack widths.
The task is solved by the invention in that at least one side stop is formed as a side guide surface which automatically compensates within a narrow tolerance range for different thicknesses of the stacked printed products passing through, and a stop returnably movable within this tolerance range always lies tightly on an outlet slot of the slot nozzle for the adhesive in the slip surface. Special and further developments of the adhesive application station are the subject of dependent claims.
As a stack always contains the same number of printed products which are cut from the same print carrier web, the tolerance ranges are from experience very narrow. Even in large stacks they are normally maximum approximately xc2x10.5 mm, in exceptional cases maximum xc2x11 mm.
In practice the most economic solution is to form an application head with a fixed stop and a stop which is resilient within the tolerance range for the stacked printed products to be bound. The advance of the stack is preferably facilitated in that the guide surfaces in the insertion direction taper to the area of the slot nozzle. This can be achieved in the form of chamfers but also by suitably curved surfaces.
The stop which is resilient in the slot direction with a guide surface can be structured according to various variants irrespective of whether a fixed stop is formed or whether both stops are resilient:
According to a first variant, a guided carriage, resilient as a whole, can be moved on a nozzle block of the application head in the direction of the outlet slot and with its guide surface form a resilient stop.
In a further variant a suitably cylindrical roller movable in the slot direction in a positionable holder and with an axis perpendicular to the slip surface, can be the guide surface.
In a variant a slide guided in the slot direction is formed with a correspondingly shaped front guide surface. The slide is movable in the direction of the guide slot, for example against the resistance of a spring or against a pneumatic pressure, and arranged in a precisely positionable retainer.
According to a last variant mentioned here, a leaf spring is arranged at the front on a positionable holder already mentioned, so that it forms a guide surface deformable resiliently by approximately xc2x11 mm in the slot direction. Various types of leaf spring are suitable which simultaneously cover the outlet slot in the tolerance range of approximately xc2x11 mm.
As already indicated, the movable stop is automatically returnable preferably by spring force. In the same way the movable stop can be pneumatically sprung. As the necessary tolerance range as has been stated is very narrow, and usually only amounts to fractions of a millimeter, the movable stop must be positionable precisely.
Furthermore, the movable stop lying on the adhesive outlet slot must cover this so well that no adhesive strings form on the bound stack of printed products. As the stops with the side guide surfaces, except for the variant with a leaf spring, can be formed more or less solid, this is in principle no problem. A short insert or thickening in a late spring can also fulfil this purpose.
The slot nozzle is formed by co-operation between the adhesive outlet slot with a metering shaft arranged tightly immediately below which for example has a diagonal longitudinal through-slot. The metering shaft in turn borders an adhesive reservoir formed as a pressure chamber which is arranged in or below the application head and in direct connection with an adhesive dispenser, for example a pressure vessel. This has the advantage not previously achieved that the adhesive, from the pressure vessel to the outlet slot in the application head, never makes contact with the air, which prevents the chemical and physical changes mentioned initially.
To create the necessary pressure in the adhesive dispenser, in a preferred variant a direct action plunger of a pressure cylinder is provided in a pneumatic accumulator. The necessary pressure can, however, also be generated hydraulically, electromagnetically or with a spindle.
The pressure can be and is changed in relation to the machine speed.
For the use of a hot adhesive, in particular a hot melt, arranged in the adhesive reservoir is at least one heating cartridge which is suitably sensor-controlled. By means of a temperature sensor, the adhesive is held at the temperature necessary for optimum viscosity.
After each discharge of adhesive through the outlet slot, automatic pressure compensation, known in itself, takes place which is integrated in the system with the pneumatic accumulator.
All stops with the guide surfaces for the stack of printed products to be bound preferably consist of wear-resistant polished material as the print media drawn over these, in particular paper, acts as an abrasive cloth. Special steels, hard metals, ceramic materials or cermets are suitable materials for guide surfaces.